This invention relates to electrical motors and specially to motors adaptable to direct energization with AC power, as the most widespread source of modern technology of power transmission, and having the capacity fo operate at no load speeds independent of the AC power frequency. The main object was to design motors with the most desirable DC meter characteristics, but without using the commutator, a part of conventional DC meters, which is the source of a plurality of eventually unavoidable problems, including more maintainance and a short trouble free life. These problems are so popular that it is not warranted to cite them here. The most robust rotor, known to the art, is the almost standardized squirrel cage rotor, and this invention uses exclusively such rotors. A further object of the invention: to construct motors with windings easy to reproduce on machines, and to control them with known means developed for commutator motors. Such means are: rheostats in series with field windings for shunt type motors, rheostats parallel to the field windings for series type motors, and control of the energy introduced into the energizing starter windings. The design of the new meters is not limited to size or voltage.
The fundamental ideas of the invention are:
(1) The appreciation that a squirrel cage rotor can be energized by induction as a member of an independent closed ferro-magnetic path including said rotor said path including two airgap crossings of the airgap surrounding a rotor on two diametrically opposite spots of the rotor circumference. Ferro-magnetic yoke closing said path beyond said crossings, and for instance by a solenoidal winding embracing said yoke. Such system represents really a short circuited transformer comprising said winding which functions as the primary, and said rotor as the secondary short circuited winding. The fundamental theory of transformers teaches that the resulting flux of the primary and secondary winding, when the secondary is shorted, becomes a small fraction of the primary flux, which appears on the primary, for instance, say with the secondary open. This phenomenon can also be explained elementary, by the law of Lenz, namely that secondary ampere turns, generated by the primary (ampere turns), are opposing the latter. As will be easily verified later, the direction of currents in the rotor bars distributed on the perifery is, for instance in a two pole motor, quite analogous and similar to the conductor currents of a two pole commutator drum rotor, with the important difference that the winding circuit having in the rotor two parallel branches closes in the rotor with commutator through the positive and negative brush, whereas in the squirrel cage rotor of my invention, through the peripheral two rings which are shorting all ends of the conductive rotor bars.
A squirrel cage rotor is equivalent and historially derived from a drum rotor having a winding of diametrically chorded coils, in all directions of the full angle and each shorted in itself. The stator induces in such equivalent rotor winding an EMF, regardless if the latter is revolving or standing, because by rotation said coils are replacing permanently each other. This replacement is analoguous to the commutator function.
(2) the appreciation that every commutator motor can operate when the current directions of both, the exciting and energizing currents respectively of stator and rotor are reversed simultaneously, and that such motor can operate on alternating positive and negative pulses or as well on alternating sinusoidal currents.
(3) the appreciation that the exciting magnetic flux of a commutator rotor is generated independently in an independent magnetic circuit whereas the same rotor is subjected to a second flux, the so called flux of the rotor reaction, generated by rotor currents in a direction perpendicular to the exciting flux lines (axis of the neutral zone).
(4) finally it is to appreciate that a single phase squirrel cage rotor is revolving with the aid of a rotating field generated by two single phase fields in quadrature, as it is well known from the accepted theory of single phase motors, one said field generated in the stator of said motor, the other (the quadrature field) by the rotor itself during rotation, and distinctly in the rotor conductors rotating in the stator field, by an electro motive force of rotation, in phase with said stator field. It is absolutely necessary for the establishment of a uniform rotating field that the reluctance presented to said quadrator field is in the same order of magnitude (preferably equal) as that of the stator field. The motor will come immediately to rest, should said reluctance to the quadrator field be substantialy increased.
The motors of this invention operate without the aid of rotating fields, through some irregular parasitic rotating fields may establish themselves during rotation. The reluctance to both, the stator and rotor fields, respectively TO the exciting and energizing flux, are by fundamental design propositions substantially different, and they are independent from each other.
Stator and rotor circuits for the generation of said fluxes can be in parallel or in series, as in commutator machines, whereas the angle defining the mutual inclination in space can be changed by one of the presented specie from quadrator to an other inclination, in analogy to repulsion motors, which work with brushes shifted out of the neutral axis.
(5) One must also observe that the torque in every motor is proportional to the differential change of mutual inductances of stator and rotor and to the currents in both. By placing the shorted brushes in a repulsion motor in the quadrature axis (neutral zone) there will be no torque developed, because no current can flow in the rotor and in the shorted commutator brushes because the induced currents in the rotor, to the left and the right of the stationary axis of energy transfer are counter balancing each other. On the other hand by placing the shorted brushes in the said axis of energy transfer, the shorted connection between the brushes will carry heavy current, as in a short circuited transformer, but there will be again no torque, because by rotation the mutual inductance of stator and rotor coils to the left and right of the energy transfer axis does not change. Placing the brushes in an intermediary position torque is present. Based on this fact Atkinson developed his motor by leaving the short circuited brushes in the neutral zone, but spliting the stator winding in two groups, one having the axis in the neutral zone, the other in quadrature to it; this invention, including several other features and innovations of the stator structure, in most resembling the Atkinson motor, but having a commutator rotor with brushes replaced by a shot circuited rotor.
(6) It is to recall from the operation of a one phase "universal motor" with commutator, that two EMF's (electro motive forces) are active in the rotor, namely the "transformer" EMF induced by an energizing flux, and one EMF derived from "flux cutting" or rotation, generated in the armature conductors in analogy to the "back" EMF of DC motors; both EMF's do have the same frequency, they are displaced in phase for 90.degree., but while the transformer EMF is independent of speed, the EMF of rotation is proportional to speed.
The new proposed motor is a combination design of (1) a repulsion motor, of the type Atkinson, (2) of an universal motor, whereby both having replaced the commutator rotor by a squirrel cage rotor and (3) of a common induction motor, but as will be explained in detail later, starting and running by induced currents stemming from the stator, which must have the same phase (direction) as in the common DC motor. The possibility of such replacements is derived from the realization that both behave similarly exposed to a one phase AC field.
Summarizing: the rotors of the said 3 AC motors do have a common feature: two types of EMF's are induced in them, both in quadrature, this phenomenon is due to the circular axial symmetry of both types of rotors, but while the induced currents close in the commutator rotor through brushes, they close in the squirrel cage rotor through the shorting side rings mounted on the bases of the cylindrical rotor drum.
As will be explained later it will be evident that the novel electro magnetic device when driven as generator can be used as Tachometer, and functions in analogy to devices known as "Amplidyne" and "Synchro-s".